Franz Ernst Neumann

mineralogist and physicist

Neumann's Law: the molecular heat of a compound is equal to the sum of the atomic heats of its constituents.^[1]

Augustin Louis Cauchy, and succeeded in deducing laws of double refraction closely resembling those of Augustin-Jean Fresnel.^[1] In studying double refraction, with his deduction of the elastic constants (on which the optical properties depend) Neumann employed the assumption that the symmetry of the elastic behavior of a crystal was equal to that of its form. In other words, he assumed that the magnitudes of the components of a physical property in symmetric positions are equivalent. This assumption substantially reduced the number of independent constants and greatly simplified the elastic equations. However, four decades passed before Neumann elaborated his application of symmetry in a course on elasticity in 1873. This principle was later formalized by his student Woldemar Voigt (1850–1918) in 1885: "the symmetry of the physical phenomenon is at least as high as the crystallographic symmetry", which became a fundamental postulate of crystal physics known as Neumann’s principle. In 1900, Voigt attributed this principle to Neumann's 1832 paper even though, at most, all that was present in that work was an implicit assumption that the symmetry of the phenomenon was equal to that of the crystal. Bernhard Minnigerode (1837–1896), another student of Neumann, first expressed this relation in written form in 1887 in the journal Neues Jahrb. Mineral Geol. Paleontol. (Vol. 5, p. 145).^[2]

Gustav Robert Kirchhoff who formulated Kirchhoff's Laws on the basis of his seminar research. This seminar was the model for many others of the same type established after 1834, including Kirchhoff's own at Heidelberg University

Halle; his younger son Franz Ernst Christian Neumann